Work-supporting means for semiautomatic electrostatic printing system



Nov. 12, 1968 J. w. EDWARDS ET AL 3,410,210

WORK-SUPPORTING MEANS FOR SEMIAUTOMATIC ELECTROSTATIC PRINTING SYSTEM Original Filed June 11. 1965 5 Sheets-Sheet 1 FIG! INVENTORS JAMES w. EDWARDS SHELLY w. MAYS, JR. HARRY J. LARRIGAN ATTORNEY Nov. 12, 1968 J. w EDWARDS ETAL 3,410,210

WORK-SUPPORTING MEANS FOR SEMIAUTOMATIC ELECTROSTATIC PRINTING SYSTEM 1965 5 Sheets-Sheet 3 Original Filed June 11.

FIG. 2

mvcmoas JAMES w. EDWARDS SHELLY w. MAYS JR. BY HARRY J. LARRlAN ATTORNEY Nov. 12, 1968 .1 w EDWARDS E AL 3,410,210

WORK-SUPPORTING MEANS FOR SEMIAUTOMATIC ELECTROSTATIC PRINTING SYSTEM 5 Sheets-Sheet 5 iginal Filed June 11. 1965 m0 mm mm mm ATTORNEY m R om m m sd wmmm mm m w J S WY ELR M m v an Y B 0 mm 8 8 w 3 N wm 5 T 2v 3 mm o 0 mm mm Q I E 8 O 9 o Q 5 mm 8 xm x Q 5 w 9 w? 0? on mm 5 Nov. 12, 1968 J. w. EDWARDS E AL 3,410,210

WORK-SUPPORTING MEANS FOR SEMIAUTOMATIC ELECTROSTATIC PRINTING SYSTEM Original Filed June 11. 1965 5 Sheets-Sheet 4 E FIG. 5

zz/ W 24 WM gg M INVENTORS JAMES W. EDWARDS SHELLY w. MAYS JR. HARRY J. LARRlAN ATTORNEY Nov. 12, 1968 J w EDWARDS ET 3,410,210

WORK-SUPPORTING MEANS FOR SEMIAUTOMATIC ELECTROSTATIC PRINTING SYSTEM 5 Sheets-Sheet 5 Original Filed June 11. 1965 FIG. 8

INVENTORS JAMES W. EDWARDS SHELLY W. MAYS, JR. HARRY J. LARRIGAN AT TO R NEY United States Patent 3,410,210 WORK-SUPPORTING MEANS FOR SEMI- AUTOMATIC ELECTROSTATIC PRINT- ING SYSTEM James W. Edwards, Creve Coeur, and Shelly W. Mays, Jr., and Harry J. Larrigan, St. Louis, Mo., assignors to Monsanto Company, St. Louis, Mo., a corporation of Delaware Original application June 11, 1965, Ser. No. 463,109, now Patent No. 3,302,560, dated Feb. 7, 1967. Divided and this application Nov. 9, 1966, Ser. No. 593,202

6 Claims. (Cl. 101-407) ABSTRACT OF THE DISCLOSURE A mandrel for holding thin-walled containers by means of a vacuum. The mandrel is rotatably mounted on a hollow shaft which merges into an end wall formed on the mandrel. An aperture is formed in the end wall communicating with the hollow shaft which is in turn connected to a source of pneumatic pressure. A plurality of radially spaced teeth circumferentially extend around the aperture and are adapted to engage the inner surface of the container bottom wall when the container is disposed upon the mandrel. The teeth will prevent an air flow past the bottom wall of the container thereby preventing the collapsing of the small portion of the bottom wall.

This application is a division of my application Ser. No. 463,109, now Patent No. 3,302,560, filed June 11, 1965.

This invention relates in general to certain new and useful improvements in electrostatic printing, and more particularly, to an improved semi-automatically operable printing apparatus for electrostatic screen process printing on a mass-production basis.

The presently known techniques in electrostatic printing are described in United States Letters Patent No. 3,081,- 698 which relates to a method of electrostatic printing by elimination of pressure or contact between the printing element and the subject material being printed. This technique involves the transfer of a liquid based ink or a resinous based ink through an electrostatic field to an image-receiving media. The ink or pigments are usually in the form of a fine powder having a particle size which is small enough to pass through the interstices of the open areas of a stencil or so-called screen. A roller or similar mechanical device normally carries the ink particles to a point in close proximity to the stencil and where the ink is carried through the stencil by the electrostatic field to the image-receiving media. When the voltage is applied to the roller or element carrying the pigment, the particles acquire a charge which is that of the stencil or screen. The charge is opposite to the backing plate and the ink particles are therefore accelerated through the openings or interstices in the open areas of the screen and toward the image-receiving media. The image-receiving media may consist of a mandrel which serves as a counter-electrode and which is capable of retaining the article to be printed. Thereafter, the pigment will collide with and adhere to the article which is to be printed and the image is subsequently fixed by heat or solvent or a vapor or by other suitable means which are known in the prior art.

Since the initial development of the theory of electrostatic printing, there have been many attempts to produce devices which are capable of automatic printing. Moreover, there have been attempts to print non-lineraly shaped articles by electrostatic methods. However, all of the attempts to produce these automatic and semi-automatic devices for electrostatic printing have been rather unsuccessful and commercially unfeasible for a number of reasons. All of the electrostatic printing devices thus far 3,410,210 Patented Nov. 12, 1968 employed have involved the transfer of ink across a definite and appreciable space and the particles of ink had to be physically transported across this space. However, surface tension effects on the delivery roller often prevented an even and uniform distribution of ink flow. Accordingly, the devices of the prior art had to be constructed in such a manner that the field across which the particles moved had an extremely large potential difference. Moreover, the various electrodes had to be specially designed in order to prevent uneven distribution and flow of ink particles.

Moreover, the devices of the prior art were not designed with a wide range of utility, and accordingly, were not capable of printing With a wide variety of types, colors and ink particle sizes. Relatively heavy electron space currents were used to assist in the movement of ink in order to attain even distribution with various sized particles of ink. However, the relatively high ionization level at the air gap for printing often causes arcing which interferes with and materially reduces the overall efficiency of the electrostatic printing device. Furthermore, with the devices of the prior art, it was difficult to achieve a carefully controlled quantity of electricity for effecting optimum results of the transfer of ink to the article being printed. As a result thereof, the devices of the prior art were not suitably designed for mass-production printing operation.

Heretofore, when hollow articles of a non-conductive material such as for example, ceramic, glass and plastic articles were to be printed electrostatically, the article had to be mounted upon an extended metallic form-fitting electrode supported upon and being electrically connected to the spindle of an electrostatic printing system. This type of construction was satisfactory in some operations. However, many of the articles to be coated vary in sizes and shapes and called for correspondingly varying conforming plate electrodes. The substitution of a plate electrode for flat items was not an expensive or time consuming procedure. However, there is no presently available device which is capable of accepting a large number of mandrels or article supporting spindles. It is not a particularly difiicult function to change a mandrel, but the devices presently available are not designed to accommodate a mandrel of a different size or shape. Electrostatic screen process printing involves accurate positioning of the electrodes within very close tolerance limits and these devices are not adaptable to such positioning.

It is, therefore, the primary object of the present invention to provide an electrostatic printing apparatus which is capable of electrostatically printing a large variety of articles having varying sizes and shapes.

It is another object of the present invention to provide an electrostatic printing apparatus of the type stated which is capable of achieving a high degree of printing precision on a mass production basis.

It is a further object of the present invention to provide an electrostatic printing apparatus and method of the type stated which is characterized by simplicity, dependability, ruggedness and low cost.

It is also an object of the present invention to provide an electrostatic printing apparatus of the type stated which is capable of being altered for employment in a multicolor printing system.

It is an additional object of the present invention to provide a method of performing printing by electrostatic screen processing techniques and which requires a minimum amount of manual attention.

It is another salient object of the present invention to provide an electrostatic screen process printing apparatus of the type stated which is adaptable for printing on articles having curvilinear shapes.

It is yet another object of the present invention to provide an electrostatic screen process printing apparatus of the type stated which is capable of automatically reversing electrostatic field polarity after each printing cycle for removal of excess electroscopic ink from the printing screen.

With the above and other objects in view, our invention resides in the novel features of form, construction, arrangement and combination of parts presently described and pointed out.

In the accompanying drawings:

FIGURE 1 is a front elevational view of an electrostatic printing apparatus constructed in accordance with and embodying the present invention;

FIGURE 2 is a rear elevational view of the electrostatic printing apparatus of FIGURE 1;

FIGURE 3 is a right end elevational view of the electrostatic printing apparatus of FIGURE 1;

FIGURE 4 is a top plan view of the electrostatic printing apparatus of FIGURE 1, rotated in a 90 counterclockwise direction for clarity;

FIGURE 5 is a fragmentary sectional view taken along line 5-5 of FIGURE 3 and showing the deails of the rotary table forming part of the electrostatic printing apparatus;

FIGURE 6 is a fragmentary sectional view taken along line '66 of FIGURE 1 showing the details of the mandrel forming part of the electrostatic printing apparatus;

FIGURE 7 is an enlarged sectional view showing the interior construction of the cup supporting mandrel forming part of the electrostatic printing apparatus of the present invention;

FIGURE 8 is a schematic view showing the electrical and pneumatic control circuit forming part of the electrostatic printing apparatus; and

FIGURE 9 is an enlarged sectional view of the mandrel of FIGURE 8.

The art of electrostatic printing is still a recent technological innovation, and the terminology peculiar to this technology has not yet achieved a commonly acceptable and understood usage and definition. Accordingly, the term printing as used herein, is employed to describe the operation of delivering ink from the ink member to the element being printed, although it is to be understood that the word printing as used herein does not connote any mechanical pressure. The word printing is used in its much broader sense of the word merely to mean transfer of a design from one element to another in analogous form to the use of the term printing in photography where mechanical pressure is not the cause of transference of the design. In interpretation of the specification and the following claims, all terminology borrowed from the conventional printing art must therefore be given a broad meaning appropriate to this specialized field of electrostatic printing.

GENERAL DESCRIPTION Generally speaking, the present invention is concerned with an apparatus and a method for electrostatic printing which is semi-automatic in its operation. The apparatus generally comprises a base with a supporting frame and upwardly mounted on the supporting frame is a suitable mechanism for retaining the ink delivery system described in copending application Ser. No. 453,706, now Patent No. 3,339,483, filed May 6, 1965. The supporting mechanism is provided with a turntable which is capable of rotating with respect to an oscillating screen. The mechanism for supporting the ink feeding system is also provided with an elevating mechanism for raising and lowering the ink feeding system. Similarly, mounted on the elevating mechanism is a pivotal support for angularly positioning the ink feeding device with respect to the screen. The, ink feeding mechanism as previously mentioned, is substantially similar to the ink feeding mechanism described in the aforementioned copending application and includes a 'hopper with an agitator for maintaining the electroscopic ink in a levitated state. The ink is thereafter deposited on a distributor roller which, in turn, deposits the ink on a continuously rotating belt. The belt is trained around a pair of rollers, one of which is electrically charged and serves as the printing electrode.

Also mounted on the supporting frame is an electric motor with suitable gear reducing means and a system for driving an oscillating screen frame. The screen frame is provided with a screen or stencil having a screen mesh section, a portion of which has been masked and a portion of which is open permitting electroscopic ink particles to pass therethrough. The screen is normally formed of a conductive material or material which is rendered conductive.

An oscillating shaft is operatively mounted on the supporting frame and is suitably powered by an air cylinder. The shaft oscillates and carries therewith a cup supporting mandrel which contains an element designed to retain thin-walled thermoformed plastic containers. A vacuum system is used to draw the cup toward and retain the cup on the mandrel, and an air system is used to shift the oscillating shaft with the mandrel. Moreover, an electrical system is provided for actuating the screen, the feeding system and the mandrel in timed relationship.

DETAILED DESCRIPTION Referring now in more detail and by reference characters to the drawings which illustrate a preferred embodiment of the present invention, A designates an electrostatic printing apparatus generally comprising a base plate 1 and welded or otherwise rigidly secured to the upper surface thereof is a table-forming support frame 2 con sisting of four spaced uprights 3 and a top plate 4.

A rotary table 5 having an attachment plate 6 is bolted or otherwise rigidly secured to the upper surface of the table forming frame 2. The rotary table 5 is provided with a longitudinally shiftable mechanism 7 consisting of a mortise 8 rigidly mounted on the attachment plate 6 and a tenon 9, which form a dovetail slide 10. The mortise 8 is integrally formed with an upstanding flange 11 for threadedly accommodating a threaded section of a jack shaft 12. The jack shaft 12 is threaded at least for a length which is sufficient for the movement of the longitudinally shiftable mechanism 7. By reference to FIGURE 5, it can be seen that the jack shaft which extends through each transverse end of the tenon 9 is rotatable in the transverse ends of the tenon 9 by bushings (not shown) which serve as radial bearings. The jack shaft 12 is retained by means of thrust washers which serve as a thrust bearing surface, and lock nuts (also not shown). The method of retaining the jack shaft 12 in the tenon 9 is conventional in its construction, and is therefore neither illustrated nor described in detail herein. At its outer end, the jack shaft 12 is provided with a bell crank handle 13 for rotation thereof. Thus, it can be seen that when the bell crank handle 13 is rotated, the threaded section of the jack shaft 12 which passes through the internally threaded upstanding flange 11 thereby longitudinally shifts the tenon 9. By means of the above outlined construction, it can be seen that the jack shaft 12 will shift longitudinally with the tenon 9.

A laterally shiftable mechanism 14 including a mortise 15 and a tenon 16 together form a dovetail slide 17 which is mounted on the longitudinally shiftable mechanism 7. By reference to FIGURE 1, it can be seen that the tenon 16 is welded or otherwise rigidly secured to the upper surface of the tenon 9. The tenon 16 is also provided with an integrally formed upstanding flange 18 which is apertured and internally threaded to accommodate a jack shaft 19 having a threaded portion 20. By reference to FIGURE 5, it can be seen that the jack shaft 19 extends through each of the ends of the mortise 17 and is journaled therein. The method of journaling the jack shaft 19 is similar to the method employed for journaling the jack shaft 12 and is, therefore, neither illustrated nor described in detail herein. At its outer end, the jack shaft 19 is provided with a bell crank handle 21. It should be understood that the threaded section has a length which is sufficient to cover the entire lateral shifting movement of the laterally shiftable mechanism 14.

Welded or otherwise rigidly secured to the upper surface of the mortise 15 is a stationary support wheel 22 forming part of a rotary table mechanism 23 which also includes a rotatable plate 24. The stationary wheel 22 is provided with an annular upstanding flange 25 having upper bearing surfaces 26 which match similar lower bearing surfaces on an annular recess 27 formed on the rotatable plate 24, substantially as shown in FIGURE 5. Integrally formed with the rotatable plate 24 on its undersurface is a depending boss 28 and rigidly secured thereto by means of screws 29 is a worm wheel 30 which is rotatable by means of a worm shaft 31. By reference to FIGURE 5, it can be seen that the worm shaft 31 extends upwardly of the support wheel 22 and is journaled therein in any conventional manner. The method of journaling the worm shaft 31 is similar to that employed in journaling the jack shafts 12 and 19 and is, therefore, neither illustrated nor described in detail herein. However, it should be noted that the worm shaft 31 is provided with a bell crank handle 32 at its upper end for rotation thereof.

Welded or otherwise rigidly secured to the upper surface of the rotatable plate 24 is an upstanding pivot arm 33 and pivotally secured thereto through a pivot pin 34 is a support frame 35 having a depending pivot flange 36, substantially as shown in FIGURE 3. The support frame 35 is generally formed of a standard U-shaped channel, preferably of stainless steel. Also welded or otherwise rigidly secured to the upper surface of the rotatable plate 24 in longitudinally spaced relation to the pivot arm 33 is an upstanding bolt 37 and which is sized to pass through an aperture (not shown) formed in the support frame 35. The support frame 35 is retained between a pair of locking nuts 38 mounted upon the opposite side of one of the flanges integrally formed with the frame 35 in the manner as shown in FIGURE 3. Thus, by adjusting each of the locking nuts 38 it is possible to pivot the support frame 35 about the pivot arm 33 and thereby adjust the support frame 35 to any desired angle with respect to the rotatable table mechanism 23.

Rigidly secured to the upper surface of the support frame 35 by means of bolts 39 is an ink feeding mechanism 40 of the type described in copending application Ser. No. 453,706, filed May 6, 1965. The support frame 35, however, is insulated from the remainder of the electrostatic printing apparatus A in any conventional manner and, therefore, the ink feeding mechanism 40 is insulated from the apparatus A, for reasons which will presently more fully appear. The ink feeding mechanism 40 generally comprises a base plate 41 and adjustably secured to the upper surface thereof near one transverse end, is an upstanding bracket 42. Pivotally mounted on the upper end of the support plate of the upstanding bracket 42 is a support plate 43 which is adjustably positioned by means of a bolt 44 secured to the opposite transverse end of the base plate 41 with a locking nut 45. Thus by turning the locking nut 45, it is possible to adjust the position of the plate 43 with respect to the horizontal.

Adjustably secured to the rearwardly presented surface of the support plate 43 is an ink hopper 46 which is provided with a pair of elongated bolts extending through a slot 48 formed within the support plate 43. The bolts are retained by a locking nut (not shown) on the forwardly presented face of the support plate 43 and which engage a retainer plate 49 in the manner as shown in FIGURE 1. The ink hopper 46 may be molded or formed of any suitable synthetic resin or plastic material. The material selected for construction of the hopper is not necessarily limited to a plastic or synthetic resin material but should be formed of material which is inert with respect to the ink contained within the hopper 46. Thus by means of the above outlined construction, it can be seen that the hopper 46 can be adjustably positioned on the support plate 43. The hopper 46 is provided with an open upper end sized for the accommodation of a removable cover plate 50 and the hopper 46 is also provided with an internal chamber 51. The details of construction of the hopper 46 are more fully described and illustrated in the aforementioned copending application relating to the ink feeding mechanism. However, it should be pointed out that an agitator 52 is operatively mounted within the hopper 46 and is designed to feed ink through a distributing roller 53 to an ink transporting belt 54. The distributing roller 53 and the ink hopper 46 are also insulated from the support frame 35 and the remainder of the ink feeding mechanism 40 all for reasons which Will presently more fully appear. The belt 54 is trained around a pair of rollers 55, 56, the roller 55 serving as a drive roller which is operable by an electric motor 57 through a drive belt 58. The roller 56 serves as a charging electrode creating an electrostatic field between a screen and a counter-electrode in a manner hereinafter described. A supporting roller 59 is disposed immediately beneath the feeding roller 53 and maintains the belt 54 in close contact with the distributing roller 53. In this connection, it should be understood that the distributor roller 53 is provided with a relatively thick bristle :brush fabric on its annular surface, preferably formed of a mohair pile fabric. One important criterion in selecting the fabric is that it must have a different triboelectric charging potential than the ink which is contained within the hopper 46. The belt 54 is similarly formed of the same type of material, preferably a mohair pile fabric material. The distributor roller 53 is so located that the bristles on the annular surface thereof extend upwardly through a discharge slot formed in the hopper 46 and engage the fine mesh particles of electroscopic ink where the particles of ink will become deposited in the interstices of the fabric. As the distributor roller rotates it will engage the fabric of the brush and the ink particles retained in the pile fabric on the roller 53 will be picked up and carried by the belt 54.

Also adjustably mounted on the bracket 42 is a charging roller 60 which is designed to engage the upper surface of the belt 54 as it passes therebeneath. The roller 60 is provided on its outer surface with a pile fabric similar to the pile fabric employed on the distributor roller 53 and on the belt 54. The surface speed of the charging roller 60 is different from the surface speed of the belt 54 and this frictional effect creates a triboelectric charge on the ink particles retained in the interstices of the belt 54. By reference to FIGURE 3, it can be seen that the charging roller 60 and the driving roller 55 are both driven through the electric motor 57. Moreover, the agitator 52 and the distributor roller 53 are driven by an electric motor 61.

It should be understood that the various rollers and driven members in the feeding mechanism herein described can be operated by individual electric motors having variable control powered means for regulating the speed of each of the individual rotating elements such as in the manner described in the aforementioned copending application relating to the ink feeding mechanism. However, it can be seen that the ink feeding mechanism 40 is provided with a wide variety of adjustments for accurate positioning thereof in the electro static printing operation.

Any of a variety of electroscopic inks can be employed in the present invention. Generally, the electroscopic inks comprise a finely dispersed powder which is capable of being triboelectrically charged. The powder generally carries a desired pigment. A number of satisfactory powders can be employed in the present invention and each must be in a finely divided state. Suitable powders are dyed thermoadhesive resins such as rosin, gum copal, gum sandarac, ethyl cellulose, Egyptian asphalt and the like. A very satisfactory thermoadhesive powder can be produced by dissolving equal parts of ethyl cellulose and Vinsol resin in acetone together with a small amount of spirit soluble aniline dye such as Nigrosine or aniline blue and spray drying the solution to produce an extremely fine powder having substantially spherical particles. Dyed Lycopodium powder is suitable where thermoadhesive properties are not required of the powder, as is also starch, cellulose flour, powdered metal and copper powder.

Whether fusible, thermoadhesive or non-fusible powders or others are used, the particle size is preferably near the limit of definition of the eye under ordinary reading conditions. Excessive powder size contributes to graininess in appearance of the image. On the other hand, extremely fine powder may be undesirable in many instances due to its tendency to ball up or cling together in clusters. It is, therefore, desirable to use a powder in which substantially all the particles are within the size range from 2.0 to microns. If spherical powders are used, this refers to their diameters, otherwise to the largest dimension. For most purposes, it is preferred to use an equidirnensional powder particle, the sphere being the preferred form.

Welded or otherwise rigidly secured to the surface of the base plate 1 is a mounting plate 62 and bolted to the mounting plate 62 is a variable speed reversible electric motor 63, which is preferably of the explosion-proof type. The motor 6 3 is electrically connected to any suitable source of electrical current (not shown) by a suitable cord set illustrated in FIGURE 8. Rigidly mounted on a support bracket 64 which is, in turn, bolted to the motor 63 is a gear driven speed reducer 65, which is connected to the drive shaft of the motor 63. The gear reducer 65 is in turn provided with a driving shaft 66, which is connected through a coupling 67 to a screen drive shaft 68. The screen drive shaft 68 is journaled in bearings which are housed in a pillow block 69, the latter being mounted on an upstanding bracket 70, which is, in turn, bolted to the mounting plate 62 in the manner as shown in FIGURE 1. The screen drive shaft 68 is, of course, provided with set collars on opposite ends of the pillow block 69. Mounted on the outer end of the screen drive shaft 68 is a friction drive wheel or socalled friction gear 71, which is retained by set collars 72. While the friction Wheel 71 is often referred to in the art as a friction gear it should be recognized that gear teeth are not employed as the mechanism for meshing engagement. A gear having a toothed periphery cannot be employed as a fairly large tolerance exists between meshing teeth on cooperative gears. This tolerance or clearance between teeth would cause a backlash or jar to the apparatus on direction reversal of the respective gears. In this connection, it should also he noted that set collars are a desirable means for retaining the friction gear 71 on the drive shaft 68 so that the gear 71 can be shifted axially along the shaft 68 by releasing the set collars 72 as the need arises. For additional support, the drive shaft 68 can be journaled in a pillow block 73 at its outer end and which is, in turn, secured to an upstanding bracket 73', the latter being suitably mounted on the base plate 1, in the manner as shown in FIG- URE 4.

Rigidly secured to the left transverse end of the base plate 1, reference being made to FIGURE 1, is an upstanding support column 74, which may be formed of a standard I-beam, H-beam or U-shaped channel. Welded to the upper end thereof and extending inwardly with respect to the printing apparatus A is an inverted L- shaped bracket 75, which is integrally formed with a supporting gusset 75 for retaining a pillow block 76. Journaled in and extending through the pillow block 76 is a rotatable screen supporting shaft 77 and mounted on the outer end thereof is an electrostatic printing screen supporting frame 78. By reference to FIGURES 1 and 4, it can be seen that the screen supporting frame 78 is provided with an arcuate contact surface 7h which is held in meshing engagement with the friction gear 71. Thus, as the motor 63 is energized and power transmitted through the drive shaft 68, the friction gear 71 will rotate and in turn, rotate the screen supporting frame 78 therewith. As mentioned above, the motor 63 is of the reversible type and the direction of the drive shaft and friction gear 71 will be continually reversed in predetermined time intervals. These time intervals are sulficiently short so that the screen supporting frame '78 is never rotated to a position where the arcuate contact surface 7-9 moves out of contact with the friction gear 71.

Removably secured to the screen supporting frame 78 by means of screws 80 is an arcuately shaped screen retainer frame 81, which is designed to removably retain a printing element or screen or so-called stencil" 82. The frame 81 is designed so that the screen 82 is easily removable therefrom. The screen retaining frame 31 may consist of marginally aligned overlying frame members which are retained by means of the screws 80. In a modified form, the screen retaining frame 81 can be provided with an open transverse end for easy removal of the screen 82. The screen 82 is generally formed of a fine mesh conductive material which is rendered conductive and wherein the nonprinting areas are suitably masked. The non-masked portion of the screen 3?, is designed to permit pigments, in the form of fine powders, to pass through the interstices of the open areas.

The screen 82 may be constructed by any of the presently known methods of making electrostatic printing screens. One particularly effective screen is provided where the mesh material is stainless steel with 250 wires to the inch. This screen element is then provided with a photosensitive coating so that it spans all of the interstices of the screen. The sensitized screen is then exposed to an are which is preferably rich in ultraviolet light, through an interposed positive image of the desired copy. Exposure to the light is maintained for a time which is sufiicient to harden the areas where the interposed image transmits light. The coated screen is then developed to dissolve the areas of the coating which were protected from the light by the opaque areas of the film ima e,

thtilreby leaving a solid mask in the areas affected by the lig t.

Various methods of preparing the screen can be used. It is only necessary that the non-printing area be effectively masked to prevent the movement of pigment therethrough in subsequent electrostatic printing operations. This is accomplished very well by various known methods as well as the use of photosensitive coatings on the open mesh. Techniques familiar in the screen-silk process printing may also be employed in the production of stencils or screens for electrostatic printing operations. It is not necessary to have the regularity of openings of a fine mesh screen or sensitized net. The regular openings in fibrous materials and the like can be satisfactory as long as the openings in the particle size of the pigment are compatible for movement therethrough.

In many electrostatic printing operations which can be performed with the apparatus of the present invention, it has been found to be desirable to use a curved electrostatic screen. The screen 82 may also be manufactured or produced in the manner as described in my copending application Ser. No. 463,251 filed June 11, 1965, and Which relates to the method of producing curved electrostatic screens. In this method, a photosensitive emulsion is applied to a wire mesh support and held in a screen chase. The screen is then exposed to light through a photographic negative of the required print or design to be ultimately imprinted upon a substrate. A washout of the exposed emulsion leaves a positive image on the screen which can be subsequently converted to a negative image required for printing by means of electroplating. The plating adheres preferentially to the open mesh portions of the screen. Subsequent treatment with an emulsion remover such as hydrogen peroxide and various acid etches will clear the print areas leaving a negative screen in which the nonaprint areas have interstices filled with metal. The plating metal is chosen to give a final screen which is rigid but fonmable by various forming methods such as rolling and drawing. The final screen thereafter can be shaped into a desired surface which will parallel complex surfaces to be printed.

Transversely spaced from the support column 74 and rigidly secured to the base plate 1 is an upstanding mandrel supporting column 83, which can also be formed of any standard rolled form I-beam or channel. Welded or otherwise rigidly secured to one flat surface of the column 83 near the upper end thereof, is a U-shaped plate 84 and bolted to the outer surface thereof is a pair of spaced axially aligned pillow blocks 85, all as can best be seen in FIGURE 1. Journaled in and extending vertically through the pillow blocks 85 is an actuator shaft 86 which is retained by means of pairs of set collars 87 mounted on opposite ends of each of the pillow blocks 85. Rigidly secured to the lower end of the actuator shaft 86 and being pivotal therewith is a crank arm 88. Welded or otherwise rigidly secured to the forwardly presented margin of the top plate 4 is a mounting bracket 89 and bolted to a horizontally extending flange 90 forming part thereof is a cylinder retaining arm 91. Pivotally mounted on the retaining arm 91 by means of a pivot pin 92 is a mandrel actuating pneumatic cylinder 93 having a clevised end for accommodating the pivot pin 92 and supporting arm 91. The pneumatic cylinder 93 is conventionally provided with a piston 94 which is, in turn, provided at its outer end with a clevis forming fitting 95. Pivotally secured to the clevis portion of the fitting 95 through a pin 96 is a crank arm 88, which in turn, pivots the actuator shaft 86. Thus by extension and retraction of the piston 94, the crank arm 88 will pivot the actuator shaft 86 within the pillow blocks 85.

Mounted on the upper end of the actuator shaft 86 and retained by means of a set screw 97 is a knee joint or so-called knee 98, which is suitably apertured to accommodate a mandrel shaft 99, all as can best be seen in FIGURE 1 and 4. By reference to FIGURE 7, it can be seen that the mandrel shaft 99 is hollow for reasons which will presently more fully appear. Rotatably mounted on the outer end of the mandrel shaft 99 is a conically shaped cup supporting mandrel 100. The mandrel 100 is generally formed of a frustoconical shape by an annular side wall 101, thereby forming a hollow interior 102. The annular side wall 101 integrally merges into opposed walls 103 and 104, which are centrally apertured to accommodate bearings 105, 106. The bearings 105 and 106 are circumferentially disposed about a diametrally reduced portion 107 of the mandrel supporting shaft 99, all as can best be seen in FIGURE 7. The outermost bearing 106 is disposed about a lock ring 108, which in turn retains the mandrel 100 on the shaft 99. At its outermost end, the mandrel 100 is integrally formed with a cup engaging open-ended extension 109 having an inwardly presented concave surface 110. The extension 109 is centrally apertured in the region of the diametrally reduced portion 107 of the shaft 99 and is provided with a slight extension 111 beyond the outer concave surface 110. The extension 111 is provided with a plurality of radially spaced, axially extending, cup engaging fingers or teeth 112 for purposes which will presently more fully appear.

Integrally formed with the end wall 103 and extending rearwardly therefrom, reference being made to FIGURE 7, is an annular flange 113 having a reduced portion forming a shoulder 114 for accomodating a friction wheel 115, the latter being in turn retained by means of bolts 116. The friction wheel 115 is sized to frictionally engage a contact strip 117, preferably formed of a ma terial which will give a high coefficient of friction with the wheel 115 and which is suitably mounted on the outer rim of the screen retaining frame 81, substantially as shown in FIGURES 4 and 7. Thus, as the screen supporting frame 78 is rotated by the friction gear 71, and the mandrel 100 is shifted to the position where the friction wheel 115 engages the contact strip 117, the mandrel 100 will axially rotate as the screen supporting frame 78 rotates about the shaft 77.

The cup supporting mandrel 100 is designed to accommodate disposable, nestable, thin-walled, plastic cups. However, it should be understood that the mandrel 100 can be readily removed and replaced with a similar mandrel accommodating cups or containers of a different size and shape. In this connection, it should be ob vious that it is possible to provide mandrels to accommodate such containers as ice cream containers, cheese containers or any similar open-ended container of this type. Moreover, it should also be understood that the present invention is not limited to the printing of plastic containers but can be employed to suitably print containers formed of paper, paperboard, etc. In the event that it is desired to replace the mandrel 100 with a mandrel of a larger diameter, or greater length, then it is possible to shift the mandrel shaft 99 within the knee 98 to obtain the desired length thereof. Moreover, it is possible to release the knee 98 on the actuator shaft 86 by releasing the set screw 97. It is, therefore, possible to rotate the knee 98 to the desired angular position with respect to the screen supporting frame 78 in order to accommodate a larger or smaller diameter mandrel. It should also be noted, by reference to FIGURES 2 and 7, that the mandrel supporting shaft 99 is so positioned so that the conically shaped wall 101 is disposed in coplaner relationship with the outer surface of the screen 82.

The degree of movement of the mandrel shaft 99 can also be regulated through a restraining mechanism 119. The restraining mechanism 119 is mounted on the actuator shaft 86, substantially as shown in FIGURE 3. The restraining mechanism 119 consists of a pair of collars 120 retained on the shaft 86 by means of set screws. Each of the collars 120 is provided with outwardly extending arms 121, each of which is adapted to engage against contact strips 122. Thus as the actuator shaft shifts to the left, the left arm 121 will engage the left contact strip 122. Similarly when the actuator shaft 86 shifts to the right, reference being made to FIGURE 3, the right arm 121 will engage the right contact strip 122. By releasing the set screw and radially turning the collar 120, with respect to the shaft 86, it is possible to adjust the amount of radial rotation of the shaft 86 before either of the arms 121 strikes the respective contact strips 122. This will, of course, proportionally limit the shifting movement of the mandrel shaft 99.

When the motor 63 is energized, the drive shaft 68 will rotate the friction gears 71 which will, in turn, rotate the screen supporting frame 78 for a predetermined distance. At the start of a printing cycle, the mandrel 100 will be in approximate horizontal alignment with the lower margin of the screen retaining frame 81 and the mandrel will be shifted to its outermost position with respect to the screen 82 or in the so-called loading position. In other words, the cup supporting mandrel 100 will be in a position where it is capable of receiving the cup ultimately to be printed. When the motor 63 is energized by a control circuit, to be hereinafter described, it will rotate the drive shaft 68- and the friction gear 71 causing the screen supporting frame 78 to rotate in a clockwise direction, reference being made to FIGURE 4. As indicated, at the start of the cycle, the cup supporting mandrel 100 will be located at the lower margin of the frame 81. As the supporting frame 78 begins to rotate in the clockwise direction, the cup supporting mandrel will be shifted to the printing position, that is the position as shown in FIGURES 2 and 4. In this position, the mandrel 100 will be spaced a proper distance from the screen 82 in order to receive the electroscopic ink in a manner to be hereinafter described in more detail. As the mandrel reaches the margin of the screen retaining frame 81, that is the position as shown in FIGURE 4, the electric motor 63 will stop and reverse its position by means of the control system hereinafter described. As this occurs, the cup supporting mandrel 100 will be shifted away from the screen supporting frame 78 to its loading position. The screen will then rotate in a clockwise direction until the lower margin of the screen retaining frame 81 is in approximate horizontal alignment with the mandrel 100.

CONTROL CIRCUIT The control circuit for the electrostatic printing ap paratus A is more fully illustrated in the schematic perspective view of FIGURE 8. For purposes of clarity, the control circuit which consists of electrical and pneumatic components has been illustrated in a perspective view and many of the electrical lines connecting the various microswitches illustrated therein have been eliminated in order to maintain clarity. It-should be obvious, however, that it is a simple process to connect the various electrical components inasmuch as the control circuit itself is operable by a 110 volt alternating electrical current source.

The pneumatic portion of the control circuit includes a pair of feed lines 123, 124 which are connected to opposite ports of the double acting pneumatic cylinder 93. The feed lines 123, 124 are connected to a double acting air control valve 125, which is in turn connected to a suitable source of air pressure (not shown). The double acting air control valve 125 is of the solenoid actuated type where a solenoid plunger will shift the core of the valve to obtain admission of air to the desired port in the cylinder 93 and vent the other port. This type of valve is conventional in its construction and, therefore, is not described in detail herein. The hollow shaft 99 is provided at its outer end, that is the end which is nearest to the knee 98, with a standard pipe fitting capable of accepting an air line and a vacuum line. The standard pipe fitting is neither illustrated nor described in detail herein, since this element is conventional and any of a number of standard pipe fittings could be employed for the purpose of the present invention. Generally, a T-shaped fitting could be most efficiently and economically employed. This standard pipe fitting is connected to an air line 126 and a vacuum line 127, and each of which is in turn connected to conventional solenoid actuable valves 128 and 129, respectively. The valves are conventional off-on valves which are actuable through an electrical signal by means of a conventional solenoid. The solenoid actuable valve 128 is connected to a suitable source of air pressure, which may be the same source of air pressure to which the valve 125 is connected. The solenoid actuable valve 129 is also connected to a vacuum source (not shown). Thus, it can be seen that when the valve 128 is open to the source of air pressure, air will be supplied to 'the outer end of the mandrel 100. By reason of the fact that the shaft 99 is open ended, air will be passed through the extension 109 where it can be employed to forcibly eject a cup or similar container from the mandrel 100. Similar- 1y, if the solenoid actuable valve 129 is open to the vacuum source, a reduced air pressure is maintained throughout the mandrel shaft 99 and the mandrel 100 therefore is capable of retaining a cup or similar article having a similar contour and size.

The electrical portion of the control circuit is also more fully illustrated in FIGURE 8 and includes a push-button on-oif switch 130, which is electrically connected to the solenoid of the valve 125, and to the solenoid of the valve 129. A microswitch supporting plate 131 is welded or otherwise rigidly secured to the upper end of the column 83, substantially as shown in FIGURES 3 and 4. Suitably mounted on the supporting plate 131 is a limit switch 132, which is electrically connected to the solenoid of the valve 129; a motor starting limit switch 133, which is electrically connected to the motor 63; a limit switch 134, which is electrically connected to the solenoid of the valve 128 and a limit switch 135, which is electrically connected to a high voltage reversing switch 136. By reference to FIGURE 8, it can be seen that the limit switches 132 and 133 and the limit switches 134 and 135 are mounted in respective pairs. Thus, when the mandrel supporting shaft 99 is shifted to the printing position, it will actuate the limit switches 132, 133. Similarly, when the mandrel supporting shaft 99 is shifted to the cup receiving position, it will actuate the limit switches 134 and 135.

The high voltage reversing switch 136 is a four terminal, two position switch which has one set of terminals connected to a suitable source of 440 volt alternating electrical current (not shown). The other set of terminals of the switch 136 is electrically connected to the mandrel 109 and to the screen 82 in any conventional manner. Thus, it can be seen that the switch 136 maintains an electric circuit to the screen 82, the mandrel and the roller 56, which serves as a counter-electrode and thereby enables an electrostatic field to be maintained therebetween. Generally, a brush and contact roller type of construction may be suitably employed to maintain an electrical connection to the roller 56. However, this type of connection is conventional in its construction and is, therefore, neither illustrated nor described in detail here- As previously indicated, the entire ink feeding mechanism 40 with the exception of the ink hopper 46 is insulated from the remainder of the electrostatic printing apparatus A. Accordingly, the metallic frame of the entire ink feeding mechanism 40 can be electrically connected to the switch 136 and the feeding mechanism 40 will serve as one electrode in the electrostatic field. The ink transporting belt 54 must have some slight electrical conductivity in order to carry an electrical charge. In this manner, the triboelectric charge can be transferred to the ink particles from the charge of current traveling through the ink transporting belt 54.

The roller 56, screen 82 and mandrel 100 are charged in such manner so that the electric field existing therebetween is in the form of a potential gradient. The direction of the potential gradient depends on the charge of the ink particles. If the ink particles are charged positively, the electrostatic field will create a negative charge or less positive charge on the mandrel. Generally, an ideal situation exists where the mandrel can be charged in one polarity, the feeding roller can be charged at the opposite polarity and the screen maintained at the ground polarity. Thus if the ink particles were positively charged, the mandrel would be negatively charged and similarly if the ink particles were negatively charged, the mandrel would be positively charged. It is not necessary to have a positive-negative type potential gradient existing between the three aforementioned components. The potential gradient which exists may be either wholly positive or negative. Thus if the ink particles were positively charged the ink feeding roller, the screen and the mandrel could have successively less positive charges so that a potential gradient still exists and where this current is capable of moving the triboelectrically charged particles from the feeding roller through the screen to the mandrel.

It can be seen by reference to FIGURE 8 that the high voltage reversing switch 136 is designed to reverse the potential gradient existing between the roller 56, the screen 82 and the mandrel 160. For example, if the mandrel 100 were positive and the feeding roller56 were negative, position reversal of the voltage switch 136 would cause the mandrel 100 to be charged negatively and the feeding roller 56 to be charged positively. If on the other hand, the potential gradient which existed was all of one charge, position reversal of the switch 136 would reverse the direction of the potential gradient. In this manner, the direction of the lines of force of the electrostatatic field 13 which exists between these various components may be reversed for removal of excess ink particles from the screen 82.

While the current requirements for electric printing of the type herein employed are not heavy in the ordinary sense, a very definite electron current or space current flows across the printing space during the printing operation. It is desirable to have a space current of at least 1 to 2 milliamperes per square inch of printing area. Moreover, the high potential source should be capable of maintaining a desired voltage under current drains in the range of approximately 100 milliamperes or slightly more.

Similarly mounted on the top plate 4 in approximate vertical alignment with the screen frame 78 are two pairs of spaced limit switches 137, 138, 139 and 140, substantially as shown in FIGURE 3 and 8. It can be seen that the pair of limit switches 137, 138 is located near the right-hand end of the top plate 4, reference being made to FIGURE 3, whereas the pair of limit switches 139, 140 is transversely spaced to the left, reference also being made to FIGURE 3. Two pairs of limit switch actuators which consists of camming elements or conventional rollers, are mounted at longitudinally spaced positions on the frame 78 and are designed to actuate the limit switches 137, 138, 139 and 140. While the limit switches are shown as being schematically mounted on the screen in FIGURE 8, it should be understood that this is only for purposes of illustrating the control circuitry of the present invention. However, it should also be understood that it is possible and convenient to mount the limit switches on the screen frame 78. This type of construction would necessitate movement of wires which are connected to each of the limit switches. Accordingly, it has been found to be more convenient to mount the limit switches on a rigid element. The limit switch 137 is electricaly connected to the solenoid of the valve 128; the limit switch 138 is connected to the motorstop switch forming part of the electrical motor 63; the limit switch 139 is also connected to the motor-stop switch of the motor 63; and the limit switch 140 is electrically connected to the solenoid actuable valve 125, all in the manner as schematically illustrated in FIGURE 8.

OPERATION In use, the hopper 46 is filled with a desired electroscopic ink. Electroscopic ink is maintained in a fluidized state or so-called fluid state and may be fluidized by any conventional process, such as passing low pressure air through a porous membrane on which the ink particles are maintained, in combination with a vibratory action. The ink in the hopper 46 is maintained in a fluidized state through the action of the agitator 52. As indicated in FIGURE 3, the agitator 52 is driven through the variable speed electric motor 61. It should also be noted that a multiwheel drive pulley could be employed for changing the ratio of the diameters of the drive wheel on the motor 61 and on the agitator 52, in order to adjust the speed thereof. Thereafter, the proper screen 82 is inserted in the retaining frame 81 and secured to the screen frame 78 through the screws 80. The screen 82 will have masked areas and non-masked areas, the latter of which permit the ink particles to pass therethrough during the electrostatic printing operation. The design of the non-masked portions of the screen 82 is therefore transferred to the article which is being suitably imprinted. Thereafter, the proper mandrel 100 is inserted on the reduced end 107 of the shaft 99. The mandrel 100 is disposed about the shaft and retained thereon by means of the lock ring 108.

Finally, the roller 56 is accurately positioned with respect to the screen 82. As previously described, the accurate positioning of the ink providing element or roller 56 herein is important in electrostatic printing operations in order to obtain fine print definition and to prevent ghosting on the cup which is to be imprinted. By rotating the bell crank handle 13 and the jack shaft 12, it is possible to shift the longitudinally shiftable mechanism 7 and the roller 56 carried therewith. Thus, it is possible to obtain the desired degree of spacing between the roller 56 and the screen 82. Similarly, it is possible to obtain the desired lateral shift with respect to the screen by rotating the jack shaft 19 through the bell crank handle 21. The portion of the jack shaft 19 in the upstanding flange 18 will shift the mortise 15 and carry therewith the roller 56. Similarly, it is also possible to angularly position the roller 56 with respect to the screen 82. This is accomplished by rotating the worm shaft 31 by means of the bell crank handle 32. Rotation 'of the worm shaft 31 will cause the plate 24 to rotate through the worm wheel 30. Thus, it is possible to accurately position the entire ink feeding mechanism with respect to the screen 82. Further fine adjustment is also possible through the various adjustment mechanisms contained on the ink feeding mechanism. For example, it is possible to position the ink hopper 46 longitudinally with respect to the screen 82 by means of releasing the elongated bolts which extend through the slot 48 and thereby shift the ink hopper 46 along the support plate 43. Furthermore, it is possible to position the relative height of the hopper 46 through the bolt 44, substantially as shown in FIGURE 3. In similar manner, it is possible to vertically positionthe roller 56 by means of adjusting the bolt 37, which elevates or lowers the entire support plate 41.

The apparatus A is designed to electrostatically print a desired image on articles which substantially have the size and shape of the mandrel 100. As indicated, the mandrel is designed to retain thin-walled, nestable, disposable cups. However, the mandrel can be changed to accommodate various sizes and shapes of articles in which it is desired to imprint a certain image. At the beginning of a printing cycle, the mandrel 100 is located in approximate horizontal alignment with the lower margin of the screen retaining frame 81 and the mandrel is shifted to its outermost position or loading position, with respect to the screen 82. When the pushbutton switch 130 is closed, a circuit is completed to the air control valve 125 and to the solenoid valve 129. Completion of a circuit to the valve 129 opens the vacuum line 127 to the hollow mandrel supporting shaft 99, thereby maintaining a vacuum within the reduced portion 107. A cup or similar article to be printed, which is held in close proximity to the outer end of the extension 109, will be pulled toward the mandrel 100. The cup engaging fingers 112 will engage the interior surface of the bottom wall of the cup, thereby maintaining a vacuum on the cup. It is to be noted that the cup engaging fingers 112 will permit an air flow thereby preventing the collapsing of a small portion of the bottom wall forming part of the container. In this connection, it should be understood that any suitable dispensing device which is capable of dispensing a single container could be employed for loading the mandrel 100 with containers at the end of each printing cycle.

The closing of the valve 125 permits air to enter the cylinder 93 through the feed line 124, thereby extending the piston 94. The crank arm 88 will rotate through the action of the fitting 95, thereby shifting the shaft 99 and the mandrel 100 carried therewith toward the screen 82. It is possible, of course, to adjust the length of the mandrel supporting shaft 99 by shifting the mandrel supporting shaft 99 within the knee 98. Moreover, it is possible to adjust the relative printing and cup receiving positions of the mandrel 100 by releasing the set screw 97 on the knee 98. The degree of movement of the mandrel supporting shaft 99 can also be regulated by means of the restraining mechanism 119 which is mounted on the actuator shaft 86. The degree of movement of the actuator shaft is adjusted by positioning of the set collars 120 so that the arms 121 strike the contact strips 122 to provide the desired degree of rotation of the shaft 86.

As the mandrel supporting shaft 99 reaches the printing position, it will strike the limit switches 132, 133. By reference to FIGURE 8, it can be seen that the limit switch 132 will close the solenoid valve 129 thereby releasing the vacuum maintained on the mandrel 100 and the cup retained thereon. However, inasmuch as the cup has a contour which is similar to the contour of the mandrel 100, it is capable of being snugly fitted thereon through the force of the vacuum previously maintained on the mandrel 100. The closing of the limit switch 133 completes an electrical circuit to the motor 63, thereby energizing the same. Energization of the motor 63 will cause the drive shaft 68 to rotate the friction gear 71 which will, in turn, rotate the screen supporting frame 78 for a predetermined distance. The screen will thereupon rotate in a clockwise direction, reference being made to FIGURE 4. It should be noted that the mandrel 100 is spaced at a proper distance from the screen 82 in order to receive the electroscopic ink as the same is delivered to the electrostatic field. It is also to be noted that the electrostatic field maintained between the roller 56 and the mandrel 100 is such that a quantity of the ink carried by the belt 54 over the roller 56 will be propelled through the screen 82 through the force created by the electrostatic field. As the screen supporting frame 78 is shifted through a complete printing cycle, the electroscopic ink which is delivered over the roller 56 will pass through the non-masl ed portions of the screen 82 thereby propelling ink through the interstices of the screen 82 to form the desired image on the cup supported on the mandrel 100. It should be noted, by reference to FIGURE 1, that the wheel 11S resides in frictional contact with the contact strip 117 when the mandrel supporting shaft 99 is moved to the printing position. As the screen supporting frame 78 rotates in the clockwise direction, reference being made to FIGURE 2, the wheel 115 will rotate the mandrel 100. Thus, as the mandrel 100 rotates in timed relation to the shifting movement of the screen supporting frame 78, a thin line of electroscopic ink will be continually passed through the non-masked portions of the screen 82 thereby forming the desired image on the container as it rotates.

As the screen supporting frame 78 continues to shift in a clockwise direction, reference being made to FIG- URE 2, or counter-clockwise direction, reference being made to FIGURE 8, the limitswitch actuator mounted on the surface of the screen supporting frame 78 will contact the limit switches 139, 140. The limit switch 139 is designed to stop the operation of the motor 63, thereby preventing rotation of the drive shaft 68 and thus stopping the movement of the screen supporting frame 81. The closing of the limit switch 140 opens the valve 125 so that air is admitted through the feed line 123 causing the piston 94 to be retracted within the cylinder 93. This will cause rotation of the actuator shaft 86 so that the mandrel supporting shaft 99 is shifted to the cup receiving position. As the mandrel shaft 99 reaches the cup receiving position, it will close the limit switches 134 and 135.

Closing of the limit switch 134 will complete a circuit to the high voltage reversing switch 136, thereby reversing the voltage applied to the screen 82, the roller 55 and the cup supporting mandrel 100, which as previously mentioned, serves as a counter-electrode. The reversing of the polarity between these three electrodes will cause any excess ink which may have gathered on the screen 82, particularly in the masked portions, to be urged back toward the roller 56. The electroscopic ink which is urged toward the roller 56 will collect on the belt 54 and cause the ink to be passed beneath the distributing wheel causing even distribution and the charging roller 60 for applica tion of a new triboelectric charge. The closing of the limit switch 134 will cause the solenoid valve 128 to open, thereby admitting air through the air line 126 and through the mandrel supporting shaft 99 to the mandrel 100, thereby forcibly ejecting the cup from the mandrel 100. It should be understood that any suitable conveyor means or cup collecting means could be disposed in close proximity to the mandrel in order to suitably collect the containers as they are ejected from the mandrel 100. This type of construction is conventional and is, therefore, neither illustrated nor described in detail herein. It should also be noted that the closing of the limit switch 135 also completes a circuit to the motor reversing switch contained within the motor 63 for reversing the operation of the electrical motor 63. Rotation thereof in the reverse direction will cause the screen supporting frame 78 to move in a counter-clockwise direction, reference being made to FIGURE 3. Due to the change of polarity between the mandrel 100 and the roller 56, the excess quantity of ink contained on the screen 82 will be pulled back toward the roller 55 in the manner previously described.

As the screen supporting frame 78 is shifted to the point where the lower margin of the screen retaining frame 81 is disposed in approximate horizontal alignment with the mandrel 100, the limit switch actuators on the screen supporting frame 78 will contact the limit switches 137, 138. The closing of the limit switch 137 will cause the solenoid valve 128 to close thereby ceasing the supply of air to the mandrel 100. Moreover, closing of the limit switch 138 will prevent energization of the motor 63, thereby stopping the movement of the screen supporting frame 78. At this position, one printing cycle has been completed and the screen supporting frame 78 and mandrel 100 are again in printing position. Thus, actuation of the pushbutton switch 130 will again start a new printing cycle in the manner previously described.

The electrostatic printing apparatus of the present invention is particularly adaptable for printing on curved surfaces in the manner described in copending application Ser. No. 472,829, filed June 11, 1965, and which relates to electrostatic screen process printing. In the printing on curvilinear surfaces such as conically shaped cups, the cup is positioned in an axis of rotation so that the exterior wall tangentially approaches and departs from the screen. Thus, the printing will occur along an elemental line of closest approach between the cup and screen. The roller 56 of the ink delivery system also tangentially approaches and departs from the screen 82 providing selected quantities of ink to the screen at the desired line of tangency. The substrate or container is rotated at approximately the same rate of speed of the movement or rotation of the screen frame 81 so that a continuing line of tangency occurs between the surface of the container and the surface of the screen 82. Simultaneously with the rotation of the screen and the container, electroscopic ink particles are moved toward and through the screen to the substrate by the electrostatic field. The ink particles are passed through the screen 82 along this line or band of tangency. In this manner, it is possible to provide electrostatically printed images on the surface of a curvilinearly shaped article, such as a conically shaped container.

It should be understood that changes and modifications in the form, construction, arrangement and combination of parts presently described and pointed out may be made and substituted for those herein shown without departing from the nature and principle of our invention.

Having thus described our invention what we desire to claim and secure by Letters Patent is:

1. An apparatus for supporting an article to be treated, said apparatus comprising a mandrel shaft which is maintained under pressure conditions, a mandrel rotatably mounted on said shaft, an end wall formed on said man- 17 that said article engaging teeth are circumferentially spaced around said aperture.

3. The apparatus of claim 2 further characterized in that said end wall has a frusto-conical shape.

4. The apparatus of claim 2 further characterized in that said mandrel has an annular conically shaped side wall, a frusto conical end wall formed with said side wall, and a substantially flat end wall formed with the other end of said side wall.

5. The apparatus of claim 2 further characterized in that said mandrel has an annular conically shaped side wall, a frusto conical end wall formed with said side wall, a substantially fiat end wall formed with the other end of said side wall, each of said end Walls having an aperture, roller means disposed in said apertures and engaging said shaft for rotatably supporting said mandrel on said shaft.

6. The appaartus of claim 2 further characterized in that a disc is rigidly secured to said mandrel and has a larger diametral size than said mandrel.

References Cited UNITED STATES PATENTS 2,425,928 8/1947 Emerson 101-38 2,484,671 10/1949 Bauman 101 3,162,115 12/1964 Bauer 101407 XR 3,273,496 9/1966 Melon 101 3,285,167 11/1966 Childress et a1. 101 3,295,440 1/1967 Rarey et al 101 3,302,560 2/1967 Edwards et al 101 ROBERT E. PULFREY, Primary Examiner.

EDGAR S. BURR, Assistant Examiner. 

